The invention relates to a system or arrangement for controlling the power output of a rotary engine in which the engine cavity has a multi-lobe peripheral profile and a rotor is rotatably supported in the engine cavity for planetary rotation relative to the axis of the engine cavity to form a plurality of working chambers between the rotor and the cavity peripheral profile which vary in volume as the rotor rotates. More specifically, the invention relates to rotary combustion engines of the type (Wankel type) disclosed in U.S. Pat. No. 2,988,065. Such Wankel type rotary engines are provided with intake and exhaust ports which are controlled by the rotor itself so that no separately movable valve elements are required to control the ports. As in the case of conventional reciprocating piston type internal combustion engines, the power output of such a rotary engine generally is controlled by a throttle valve in the intake engine passage leading to the intake port. As a result, when the engine is operating at part load, that is, when the throttle valve is partly closed, there are power losses associated with the pressure drop across the throttle valve.
U.S. Pat. No. 3,762,376 to Eberle discloses a Wankel type rotary combustion engine in which the intake port is provided with means for varying the dimension of the intake port opening in the direction of rotor rotation to vary the power output of the engine so that the engine can be operated without the aforementioned usual throttling losses. In that patent, low engine power outputs are obtained by elongating the intake port opening by means of a slide valve in a side housing of the engine so that a portion of the intake port is still open to a working chamber after the chamber has started its compression phase whereby a portion of the working fluid is pumped back through this portion of the intake port into the intake passage. This arrangement thereby introduces pumping losses into the engine. The construction of the Eberle patent has the further disadvantage in that the intake slide valve must be flush with the intermediate housing in which it is mounted to avoid leakage at the rotor side seals as they cross the slide valve. Also if the intake slide valve is not flush a substantial length of each side seal of the rotor will be unsupported as it crosses the slide valve thereby causing excessive wear of the side seals. This problem in the Eberle patent is accentuated when the intake port slide valve is wide open. Also the Eberle intake slide valve extends into the high pressure region of the engine and therefore must seal tightly in all positions in order to avoid loss of engine compression. Furthermore the intake slide valve in the Eberle patent extends out beyond the engine housing and therefore since it is slidably mounted in the face of the intermediate housing it would interfere with the housing seals usually provided between the rotor and intermediate housing to prevent leakage of the liquid coolant from the engine housing.